1. Field of the Invention
The present invention relates to a device for detection of knocking in a diesel engine.
2. Description of the Prior Art
When an ignition lag or delay is experienced in a diesel engine in a time duration from an injection beginning from which the fuel injection is started to an ignition timing at which the combustion pressure is abruptly increased, the subsequent combustion is adversely affected. As the ignition delay time increases, the amount of the air-fuel mixture obtained before ignition increases. Such an increased mixture burns at the same time to give rise to an abrupt pressure rise. This causes vibration, knocking, and the like.
Diesel knocking is attributed to a high rate of increase in combustion pressure per unit angle, i.e., dP/d.theta., where P is the combustion pressure of the engine and .theta. is the angle of the crankshaft. When the value of the rate dP/d.theta. exceeds about 5 atm/deg, knocking becomes particularly serious, adversely affecting the engine. In a diesel engine, the compression ratio is generally high. Thus, the base vibration is large and overcomes vibration of the engine block. This prevents reliable detection of knocking based on detection of vibration of the engine block unlike the case of a gasoline engine, in which the vibration level of the base is low.